cpuidle: calxeda: Add missing __iomem annotation

Added missing __iomem annotation in order to fix the following
sparse warnings:

drivers/cpuidle/cpuidle-calxeda.c:44:24: warning: incorrect type in argument 1 (different address spaces)
drivers/cpuidle/cpuidle-calxeda.c:44:24:    expected void [noderef] <asn:2>*<noident>
drivers/cpuidle/cpuidle-calxeda.c:44:24:    got void *extern [addressable] [toplevel] scu_base_addr
drivers/cpuidle/cpuidle-calxeda.c:56:24: warning: incorrect type in argument 1 (different address spaces)
drivers/cpuidle/cpuidle-calxeda.c:56:24:    expected void [noderef] <asn:2>*<noident>
drivers/cpuidle/cpuidle-calxeda.c:56:24:    got void *extern [addressable] [toplevel] scu_base_addr

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>